Summary Nowadays, Ultra-wideband (UWB) technology is gaining much attention in the field of wireless communication, mainly due to its unique capabilities and potential applications together with the large unlicensed large frequency band devoted to it. However, the design and successful implementation of UWB transmission systems require a good understanding of the propagation characteristics of the radio channel. This thesis deals with the development of realistic channel models to support UWB communication design and evaluation. Different ways exist to develop a UWB channel model. A major method, which is the focus of this thesis, is to use statistical approaches based on measurements. To this end, a time-domain measurement set-up covering the frequency band from 3.1 to 10.6 GHz has been developed. Different limitations which are specific for the time-domain measurement are highlighted and solutions have been proposed to remove these limitations. As the performance of any communication system is determined by the characteristics of the radio channel in which it operates, our measurements have been conducted in different environments e.g. indoor office, indoor industrial area, outdoor to indoor and and Wireless Personal Area Network (WPAN) environments. In order to provide a good statistical UWB channel characterization, a sufficient number of channel impulse responses (CIRs) are gathered. These CIRs are retrieved from the time-domain measured signals using an appropriate post-processing. Based on the measured data, different statistical channel models, including large, middle and small-scale fading, have been proposed for the frequency band 3.1-10.6 GHz. UWB is a promising technology for several short-range applications (e.g. WPAN, WBAN). However, in these applications the transmit and receive antennas are very close to each other and far-field antenna conditions, assumed in most available link budget models, may not be satisfied. Under the near-field conditions, variations in the link budget and pulse shape compared to the far-field can be observed. In this thesis, a new empirical UWB link budget model for short-range UWB channels is proposed and validated by measurements and simulations using different types of antennas. The proposed model includes frequency, antenna size and orientation as parameters, and shows a good agreement with the simulations and the measurements. Usually in the statistical modeling of the UWB channel, the whole UWB band is sounded. Because of the very large bandwidth, the measurement set-up becomes complex, and consequently different parameters must be taken into consideration. In this thesis, a new approach to estimate the wireless UWB channel is introduced where partial information of sub-band channels is available (measured) and used in the estimation process. Positioning information in indoor environments is becoming more important and attractive, especially for wireless ad-hoc networks and area dependent wireless services. One of the main issues in positioning is how to achieve a good range estimation. Usually, the required range accuracy depends on the application and can vary from a few centimeters to tens of meters. UWB radio seems to be a promising solution for achieving a high accuracy. The last part of this thesis deals with the application of UWB technology for ranging/positioning. For instance, different methods based on time of arrival or signal strength, to estimate the range in dense indoor multipath environments are evaluated@en

Wireless personal area networks applications may benefit from the use of ultra-wideband (UWB) technology. In these applications transmit and receive antennas are very close to each other and the far-field condition assumed in most of the link budget models may not be satisfied. Under near-field conditions, variations in the link budget and pulse shape compared to the far-field can be observed. In this work, a new validated with measurements using different types of antennas. The measurements have been performed in the time domain by exciting the antenna with very short pulse of 35 ps width covering a large frequency band. The proposed model, which includes frequency , antenna size and orientation as parameters, shows a good agreement with the simulations and the measurements.@en

In this paper, ranging based on UWB signals is investigated for indoor dense multipath environments. To this end, a large set of time domain measurements covering the 3.1-10.6 GHz frequency band is carried out. Different approaches to detect the time of arrival of the first path are evaluated. Ranging results based on time estimation are compared to those based on signal strength. Additionally, the effect of the bandwidth on the range estimates is analyzed. Generally, the results show that high ranging accuracy can be achieved for both LOS and NLOS propagation when UWB is used. Analysis of the data points out that additional delay introduced by propagation through walls is the main source of range error in NLOS indoor environments.@en

This paper presents the results of Ultra Wide Band (UWB) channel measurements carried out at the campus of Delft University of Technology. The measurements were conducted in an indoor office and industrial environment using a time domain setup which allows measurements from 3.1 to 10.6 GHz. Results on large scale path-loss exponent, shadowing, small scale fading and rms delay spread (RDS) for indoor office and industrial area propagation are presented.@en

In this paper, the results of Ultra Wide Band (UWB) measurements carried out in indoor environments are presented and a statistical propagation model for the UWB channel covering the frequency band from 3.1. to 10.6 GHz is proposed. The measurements have been performed in the time domain by exciting the channel with very short pulses of 50 ps width. Both Line-of-Sight (LOS) and on-Line-of-Sight (NLOS) propagation with a maximum distance of 10 m are considered. INspection of measeured data after processing shows that the multipath components of the UWB channel tend to arrive in clusters. Therefore, the Salch-Valenzeula (S-V) model has been adopted as starting point for our modelling analysis. Important channel parameter statistics of the model are extracted from the measured data. The obtained results show some discrepancies with respect to the IEEE channel model. The results presented here illustrate that the conventional singel Poisson proces is not sufficient to model the cluster and ray arrival times. Therefore, a Gamma distribution is proposed to model the cluster inter-arrival times and a mixture of two Poisson processes to model the ray intra-arrival times. It is found that the amplitude fading statistics can be modelled by the Log-normal distribution with a standard deviation decreasing linearly with the excess delay. Other parameters like cluster and ray power decay constants are determined to complete the statistical UWB channel model.@en

Ultra Wide Band (UWB) technnology is prome to be used in wireless personal area networks (WPAN) applications. In these applications transmit and receive antennas are very close to each other and the far field condition assumed in most of the link budget modesl may not be satisfied. Under near field conditions, variations in the link budget and pulse shape with respect to the far fiedl can be observed. In this work, near field WPAN measurements have been carried out with three different biconical antennas in order to analyze the link budget. A new link budget model is proposed and compared with the measurements. Results can be used in the design and coverage analysis of UWB communication systems for WPAN applications.@en

Integration of a miniaturized ulta-wideband antenna with an impulse generator on chip is investigated. Impedance matching between an UWB antenna and an impulse generator as well as, a proper design for the antenna feeding and minimization of the influence of the chip and chip feeding lines on antenna performance have been analyzed. The performance of the integrated antenna with an impulse generator has been verified experimentally.@en

In this paper, the impact of the noise due to undersampling of noncoherent narrowband interference in time domain UWB channel measurements is investigated. Different measurements were carried out within the building for LOS and NLOS situations. The obtained results show that energy of external narrowband interference (especially at frequencies below 3.1 GHz) is spread over the whole measured bandwidth (1-12 GHz) as a quasi-white noise. This spreading is caused by the stroboscopic sampling receiver and used in the measurement setup. The leel of this additional noise is relatively high and its suppression is required for long-distance by an analogue bandpass filter directly after the receive antenna substantially decreases the noise floor and results in a large improvement of the singal-to-noise ratio.@en

In this paper, a new method for UWB channel characterization is introduced. This method is based on the knowledge of the frequency response of several (but not all) randomly selected portions (chunks) of the UWB band. Employing this method, estimation of the root mean square (rms) delay spread (RDS) is investigated. The results for different scenarios are compared to the casewhen the complete UWB channel is known. Wideband indoor channel measurement data at 2.4, 4.75 and 11.5 GHz of [1], which fulfils the UWB criteria, is evaluated using the introduced method. The results show that the RDS of the UWB channel can be estimated when the frequency response of the UWB channel is only partially known.@en